Black carbon

Black carbon, also called soot, arises from sources such as diesel engine exhaust, burning biomass, cooking fires, and coal plants. It is made up of tiny carbon particulate matter that contributes to global warming by absorbing heat in the atmosphere and reducing albedo, the reflection of sunlight, when deposited on snow and ice. It is also a big component of air pollution around the world.

Climate change
In a paper published in May 2008 in Nature Geoscience, Carmichael and Ramanathan found that black carbon soot from diesel engine exhaust and cooking fires -- widely used in Asia -- may play a larger role than previously thought in global warming. They said that coal and cow dung-fueled cooking fires in China and India produce about one-third of black carbon; the rest is largely due to diesel exhaust in Europe and other regions relying on diesel transport. The largest source of black carbon is the burning of biomass, especially forests and grasslands.

A 2010 USAID study identified black carbon as the second or third largest contributor to the current anthropogenic global warming, surpassed only by carbon dioxide and methane. Black carbon, however, has a much shorter average atmospheric residence time than carbon dioxide. It has been found that one kg of black carbon heats the atmosphere 500 to 680 times more than one kg of carbon dioxide over a 100-year time frame and 1,500 to 2,200 times over a 20-year time frame.

The report also considered black carbon an agent for faster melting of ice in the Himalayas: "Black carbon directly heats the surface on which it is deposited and accelerates the melting of the Arctic sea and land ice, glaciers and seasonal snow covers. As per 2006 data, China is a dominant emitter of black carbon from combustion, accounting for 61 percent of all Asian emissions, followed by India at 12 percent and Indonesia at 6 percent."

To test the effect of black carbon on warming, UI College of Engineering Professors Greg Carmichael and Karl Kammermeyer conducted a study comparing ground-level air samples at Cheju Island, South Korea, with "purer" air sampled at altitudes between 100 and 15,000 feet above the ground. They found that the amount of solar radiation absorbed increased as the black carbon to sulphate ratio rose. Also, black carbon plumes derived from fossil fuels were 100 percent more efficient at warming than were plumes arising from biomass burning: "These results had been indicated by theory but not verified by observations before this work. There is currently great interest in developing strategies to reduce black carbon as it offers the opportunity to reduce air pollution and global warming at the same time," Carmichael said. The authors suggest that climate mitigation policies should aim to reduce the ratio of black carbon to sulphate in emissions, as well as the total amount of black carbon released.

Particulate matter regulations
The EPA Office of Air Quality Planning and Standards (OAQPS) has set National Ambient Air Quality Standards under the Clean Air Act for six principal pollutants, which are called "criteria" pollutants: sulfur dioxide, particulate matter, nitrogen oxides, ozone, lead, and carbon monoxide. After the EPA sets or revises each standard and a timeline for implementation, the responsibility for meeting the standard falls to the states. Each state must submit an EPA-approved plan that shows how it will meet the standards and deadlines. These state plans are known as State Implementation Plans (SIPs)."

Since 1997 coarse (diameter greater than 2.5 μm) and fine (diameter between 0.1 μm and 2.5 μm) particles have been regulated by the EPA, but ultrafine particles (diameter less than 0.1 μm) remain unregulated. Roughly 80% of the ash falls into an ash hopper, but the rest of the ash then gets carried into the atmosphere to become fly ash.

In a motion filed on December 7, 2010, the EPA asked for an extension in the current court-ordered schedule for issuing rules that would reduce harmful air emissions from large and small boilers and solid waste incinerators, which would cut emissions of pollutants, including mercury and soot. EPA is under a current court order to issue final rules on January 16, 2011 and is seeking in its motion to the court to extend the schedule to finalize the rules by April 2012. The agency said the additional time is needed "to re-propose the rules based on a full assessment of information received since the rules were proposed."

EPA finds Clean Air Act benefits will add up to $2 trillion by 2020
According to an EPA report released in March 2011, "The Benefits and Costs of the Clean Air Act from 1990 to 2020", the annual dollar value of benefits of air quality improvements from 1990 to 2020 will reach a level of approximately $2.0 trillion in 2020. The benefits would be achieved as a result of Clean Air Act Amendment-related programs and regulatory compliance actions, estimated to cost approximately $65 billion by 2020.

Most of the benefits (about 85 percent) are attributable to reductions in premature mortality associated with reductions in ambient particulate matter: "as a result, we estimate that cleaner air will, by 2020, prevent 230,000 cases of premature mortality in that year" (Introduction). The remaining benefits are roughly equally divided among three categories of human health and environmental improvement: preventing premature mortality associated with ozone exposure; preventing morbidity, including acute myocardial infarctions and chronic bronchitis; and improving the quality of ecological resources and other aspects of the environment.

According to the report: "The very wide margin between estimated benefits and costs, and the results of our uncertainty analysis, suggest that it is extremely unlikely that the monetized benefits of the CAAA over the 1990 to 2020 period reasonably could be less than its costs, under any alternative set of assumptions we can conceive. Our central benefits estimate exceeds costs by a factor of more than 30 to one, and the high benefits estimate exceeds costs by 90 times. Even the low benefits estimate exceeds costs by about three to one."

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